Crustal thickness map of the Chinese mainland from teleseismic receiver functions

Models of crustal thickness for South America from seismic refraction, receiver functions and surface wave tomography

An extensive compilation of crustal thicknesses is used to develop crustal models in continental South America. We consider point crustal thicknesses from seismic refraction experiments, receiver function analyses, and surface-wave dispersion. Estimates of crustal thickness derived from gravity anomalies were only included along the continental shelf and in some areas of the Andes to fill large gaps in seismic coverage. Two crustal models were developed: A) by simple interpolation of the point estimates, and B) our preferred model, based on the same point estimates, interpolated with surface-wave tomography. Despite gaps in continental coverage, both models reveal interesting crustal thickness variations. In the Andean range, the crust reaches 75 km in Southern Peru and the Bolivian Altiplano, while crustal thicknesses seem to be close to the global continental average (~ 40 km) in Ecuador and southern Colombia (despite high elevations), and along the southern Andes of Chile–Argentina (elevation lower than 2000 m). In the stable continental platform the average thickness is 38 ± 5 km (1-st. deviation) and no systematic differences are observed among Archean–Paleoproterozoic cratons, NeoProterozoic fold belts, and low-altitude intracratonic sedimentary basins. An exception is the Borborema Province (NE Brazil) with crust ~ 30–35 km thick. Narrow belts surrounding the cratons are suggested in central Brazil, parallel to the eastern and southern border of the Amazon craton, and possibly along the TransBrasiliano Lineament continuing into the Chaco basin, where crust thinner than 35 km is observed. In the sub-Andean region, between the mid-plate cratons and the Andean cordillera, the crust tends to be thinner (~ 35 km) than the average crust in the stable platform, a feature possibly inherited from the old pre-Cambrian history of the continent. We expect that these crustal models will be useful for studies of isostasy, dynamic topography, and crustal evolution of the continent.

Models of Crustal Thickness for South America from Seismic Refraction, Receiver Functions and Surface Wave Tomography

[1] We collected and processed a large amount of high-quality broadband teleseismic waveform data recorded by the 48 Chinese National Digital Seismic Network stations to estimate large-scale lateral variations of crustal thickness and Vp/Vs ratio (hence Poisson's ratio) beneath China. A statistical method was used to select mutually coherent receiver functions at each station, which yielded over 200 traces for most of the stations. With the conventional H−κ (the crustal thickness and Vp/Vs ratio) approach, there is a large trade-off between H and κ. Consequently, multiple maxima are frequently observed in the H−κ domain. We introduced a weight function that measures the coherence between the P-to-S conversion and the reverberation phases at each H−κ grid to reduce the trade-off. A 4th-root stacking method was further applied to reduce uncorrelated noise relative to the linear stack. These modifications turned out to be very effective in reducing the H−κ trade-off and yielded reliable estimates of crustal thickness and Vp/Vs ratio. The crust beneath eastern China is as thin as 31–33 km and the underlying Moho is relatively flat and sharp. In the western part of China, the crust is considerably thicker and shows large variations. The Moho is observed at about 51 km depth along the Tian Shan fold system and about 84 km deep beneath the central part of the Tibetan Plateau. The transition occurs at the so-called N-S belt between about 100° and 110°E, which is featured by unusually high seismicity and large gravity anomalies. The average Vp/Vs ratio over the mainland China crust is about 1.730 (σ = 0.249), significantly lower than the global average 1.78 (σ = 0.27) of the continental crust. This lower Vp/Vs ratio may suggest a general absence of mafic lowermost crustal layer beneath China.

Crustal structure beneath China from receiver function analysis

https://www.gseis.rice.edu/Reprints/R072_SunEL12EPSL.pdf

Crustal structure and deformation of the SE Tibetan plateau revealed by receiver function data

[1] We have investigated crustal thickness and composition across the southeastern Caribbean plate boundary with the receiver function technique. We used teleseismic data recorded by a temporary broadband array deployed under the BOLIVAR project and the permanent national seismic network of Venezuela. We used the primary P-to-S conversion and crustal reverberations to estimate crustal thickness and average crustal VP/VS ratio over the region. We observe large variations in crustal thickness and Poisson's ratio. Estimated Moho depth ranges from ∼16 km beneath the southeastern Caribbean Sea to ∼52 km beneath northeastern Venezuela and the Venezuelan Andes. There is a good correlation between crustal structure and tectonic terranes. Data from the Precambrian Guayana Shield suggest that the underlying crustal structure is relatively uniform with a moderate thickness (∼37 km) and an intermediate composition. A thick crust is found below the foreland basins. The two mountain systems in northern Venezuela, the Serrania del Interior and the Serrania del Falcon, have a thin crust with arc composition and are likely dynamically supported by elastic rebound or underthrusting of the oceanic plateau that characterizes the southern Caribbean. On the other hand, the Venezuelan Andes and Perija Range on the western side of the country are probably isostatically balanced by thick crustal roots.

/pdf/receiver-function-study-of-the-crustal-structure-of-the-wlbc6pshw1.pdf

Tammy Bravo

Papers

Receiver function study of the crustal structure of the southeastern Caribbean plate boundary and Venezuela